1. Field of the Invention
The present disclosure is related to a solar battery control apparatus installed in vehicle.
2. Description of the Related Art
Output power of a solar battery depends on an output characteristic (i-V output characteristic) of generated current and generated voltage varying in accordance with connected load. A point indicated by the generated current and the generated voltage in the i-V output characteristic which allows the output power of the solar battery to be maximal is referred to maximum power point (MPP).
The i-V output characteristic of a solar battery varies according to sunshine condition, etc., and correspondingly, the MPP also varies. The maximum power point tracking (MPPT) control for tracking the MPP so as to effectively acquire electric power of the solar battery is known (for example, see Patent Document 1).
In the MPPT control, usually, the MPP is searched for while varying the generated voltage or the generated current by controlling a load circuit such as a DC-DC converter connected to the solar battery. That is, in the MPPT control, usually, the generated voltage and the generated current are used as control variables for searching for the MPP.
Here, in a solar battery panel in which a plurality of solar cells are connected in series for enlarging voltage output capability, or the like, generally, a circuit configuration is adopted where a bypass diode is disposed so that the current flows bypassing a part of the solar cells in a case where the part of the solar cells are in a shadow (occurrence of a partial shadow). Therefore, upon the occurrence of the partial shadow, the generated voltage of the solar battery panel or the like may rapidly vary (decrease).
In such case, if the MPP is searched for with the generated voltage as a control variable, the MPPT control may be inappropriately performed due to the rapid decrease of the generated voltage of the solar battery panel caused by the occurrence of the partial shadow, and consequently, the generated current of the solar battery panel may become “0”, that is, the output power may become “0”. Therefore, when performing the MPPT control with the generated current as a control variable, a strong resistance against the rapid variance of the generated voltage can be obtained, which is caused by the occurrence of the partial shade with respect to the solar battery panel or the like.
However, in a case where the MPPT control is performed with the generated current as a control variable in the solar battery installed in the vehicle, problems described below may be caused.
For example, in a case where a vehicle having a solar battery disposed on a roof panel thereof is traveling on a flat road as shown in FIG. 1A to raise only its front wheels onto a step on a road as shown in FIG. 1B, a solar radiation angle to the solar battery changes from θ1 into θ2. Since the angle θ1 is greater than the angle θ2, as shown in FIG. 2A and FIG. 2B, solar radiation intensity in the solar battery decreases rapidly to cause the i-V output characteristic of the solar battery to rapidly vary in a case where the front wheels of the vehicle are raised onto the step of the road as shown in FIG. 1B.
FIG. 2A is a diagram for illustrating an example of the i-V output characteristic of the solar battery corresponding to a state of vehicle shown in FIG. 1A. FIG. 2B is a diagram for illustrating an example of the i-V output characteristic (a solid line) of the solar battery corresponding to a state of vehicle shown in FIG. 1B. Additionally, a dashed line shown in FIG. 2B shows the same i-V output characteristic of the solar battery shown in FIG. 2A.
As shown in FIG. 2A and FIG. 2B, when the state of the vehicle transitions from the state shown in FIG. 1A into the state shown in FIG. 1B where its wheels are raised onto the step, short-circuiting current in the i-V output characteristic is reduced, while a release voltage in the i-V output characteristic changes little. Then, as shown in FIG. 2B, a setting value of the generated current as the control variable becomes greater than the short-circuiting current, and consequently, the corresponding generated voltage fails to be found and becomes “0”, which causes the output power to rapidly move to “0”.
Thus, in a case where the MPPT control is performed with the generated current as the control variable, the output power from solar battery installed in the vehicle may not be stable since the i-V output characteristic of the solar battery installed in the vehicle may rapidly vary in accordance with the movement of the travelling vehicle.